1. Field of the Invention
The present invention is directed to apparatus for the automatic calibration of measuring instruments having a sensor probe that can be subject to changes in output signals and, more particularly, to an automatic calibrating apparatus that can perform the calibration on a sensor probe during a storage mode.
2. Description of Related Art
It is well known that various forms of scientific and measurement instruments require periodic calibration to the sensitivity of various components of the measurement system, such as a sensor probe. For example, a pH meter that is frequently used in laboratories and in field applications can have its electric potential and sensitivity change over a period of time, and also when subjected to various concentrations of solutions. Thus, it is required to periodically calibrate the instrument, or even to calibrate it prior to each measurement.
Referring to FIG. 3(A), an example of a conventional prior art system is disclosed wherein an electrode portion 32 is formed at the front end of an ion concentration measuring portion 31. The electrode portion 32 is washed, for example, by pure or distilled water from an appropriate pure water vessel 33, in order to remove the drops of any liquid that has adhered to the electrode portion 32. After this washing, the electrode portion 32 can be soaked in a calibrating pH standard solution 36 contained in a beaker 35, as shown in FIG. 3(B). The operator then monitors the stabilization of any indicated output value on a visual display portion 38 of the pH meter body 37, as shown in FIG. 4. In addition, the temperature of the calibration solution 36 is measured by means of a thermometer 39. The pH value at that time can be read on a table (not shown). As seen in FIG. 4, a knob or set of knobs 40 on the pH meter body 37 can then be adjusted so that the indicated value of the output display will correspond to the pH value on the reference table.
Frequently, the above procedure steps must be repeated to both reaffirm the value and to ensure an accurate reading exists.
This procedure must be carried out prior to the measurements, or at least on a periodic basis, and has a disadvantage in that it not only increases the measurement time period required, but further requires an expenditure of time, frequently by relatively skilled technicians, with an appropriate cost factor.
The prior art is still seeking to improve the accuracy and calibration procedures utilized for measurement instrumentation such as pH meters.